Concurrent Intrathyroidal Thyroid Cancer and Thyroid Cancer in Struma Ovarii: A Case Report and Literature Review

Context The presence of differentiated thyroid cancer in mature cystic teratomas in the ovaries is rare, and usually incidentally found on surgical pathology specimens. We present a case of simultaneous intrathyroidal thyroid cancer and thyroid cancer within a struma ovarii, presenting specific diagnostic challenges. Case Description A 55-year-old woman had an intrathyroidal, encapsulated 1.2-cm papillary thyroid carcinoma, follicular variant, which was resected. Laboratory studies showed an elevated thyroglobulin level of 35 ng/mL while on suppressive levothyroxine therapy. During preparation for radioactive iodine ablation, thyroglobulin increased dramatically to 3490 ng/mL. A pretreatment whole-body scan showed residual tracer uptake in the thyroid bed and increased radiotracer uptake in the pelvis that raised concern for a pelvic metastasis, given the marked thyroglobulin elevation. After ablation, the posttreatment scan showed intense focal uptake in the pelvis. Single-photon emission computed tomography-computed tomography confirmed that the tracer uptake corresponded to a right adnexal mass. The patient underwent a laparoscopic bilateral salpingo-oophorecotomy with pelvic washings. The final pathology of the right ovary showed papillary thyroid carcinoma arising in a mature cystic teratoma. In addition, there was abundant normal thyroid tissue with colloid surrounding the carcinoma, indicating a source for the dramatic rise in thyroglobulin levels and suggesting that the ovarian papillary thyroid cancer arose within the teratoma and was not metastatic disease. Thyroglobulin measurements have been undetectable for 5 years since surgery and radioiodine treatment. Conclusions Concurrent intrathyroidal thyroid cancer and differentiated thyroid cancer in struma ovarii are very rare, but can often be distinguished on clinical grounds.